Daphne Avalon/YouTube(NEW YORK) -- The undercover narcotics cop accused of assaulting the driver of an SUV in the highly publicized incident of road rage last month infiltrated the Occupy Wall Street group for police, according to law enforcement sources.

He was even "arrested" at one of their protests, one member of the group says.

Police this week charged the cop, Wojciech Braszczok, 32, with gang assault, assault and criminal mischief in connection with the Sept. 29 attack in New York City on SUV driver Alexian Lien.

But new details have emerged about Braszczok's apparent double-life as a member of the New York City Police Department. Braszczok was known within the Occupy Wall Street movement as "Al," according to the group member.

Braszczok apparently showed up at Occupy Wall Street parties and was "arrested" at a protest last year, according to the member of the group. It's unclear whether that was a bogus move to strengthen his cover.

Braszczok also maintained a Twitter account that promoted the movement's call to action, which ABC News has verified belonged to the officer.

Nicholas Casale, a former NYPD detective, says Braszczok's apparent infiltration of the Occupy movement is part of the job of being an undercover cop.

"The undercover has to be the actor," said Casale, who has no connection to this case. "He never can take on the norms, the mores, the social culture of the bad guy."

Lien's wife and 2-year-old daughter were also in the car at the time of the assault and that's where Casale said Braszczok's focus should have been.

"His loyalty should have been to the innocent man, his wife and child in the car," he said.

Braszczok initially told his superiors days after the incident that he saw the attack but did not stop it for fear of blowing his cover, police said. But video captured at the scene revealed that he actually participated by smashing the back window of Lien's Range Rover, law enforcement sources said.

Casale says there were measures Braszczok could've taken to help the Liens while concealing his true identity.

"Try to distract those who were aggressively trying to attack that car," by telling the bikers "the police are coming. Let's get out of here,'" Casale suggested.

Braszczok's attorney, John Arlia, called the gang assault charge an "absolute overcharge" and said there's no evidence the detective knew the other bikers. The riders are a loosely knit group that arranges rides via the Internet, Arlia said.

The melee unfolded when Lien tapped the back of a motorcycle that cut in front of him and slowed down, police said. The rest of the bikers then closed in on him, prompting Lien to speed off, hitting three bikers as he accelerated away from the group, according to the NYPD.

The group chased Lien and then pulled him from his car and beat him, cops said.

Police have arrested seven people allegedly connected to the incident. Five of the motorcyclists have been charged, and police said they are continuing to search for suspects.